Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $231.89   6.749%   $247.5403   $247.54   $247.55   $247.50  
  Purchase #2 $86.78   8.338%   $94.0157   $94.02   $94.00   $94.00  
  Purchase #3 $230.84   3.354%   $238.5824   $238.58   $238.60   $238.60  
  Purchase #4 $230.30   5.388%   $242.7086   $242.71   $242.70   $242.70  
  Purchase #5 $128.61   5.384%   $135.5344   $135.53   $135.55   $135.50  
  Purchase #6 $64.82   10.216%   $71.442   $71.44   $71.45   $71.40  
  Purchase #7 $18.52   8.856%   $20.1601   $20.16   $20.15   $20.20  
  7 purchase totals = $991.76       $1,049.9835   $1,049.98   $1,050.00   $1,049.90